linux-kernel - Re: [PATCH v1] dmaengine: sf-pdma: pdma

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Date:   Fri, 20 Jan 2023 10:50:01 +0000
From:   Conor Dooley <conor.dooley@...rochip.com>
To:     shravan kumar <shravan.chippa@...rochip.com>
CC:     <green.wan@...ive.com>, <vkoul@...nel.org>, <palmer@...belt.com>,
        <paul.walmsley@...ive.com>, <linux-kernel@...r.kernel.org>,
        <linux-riscv@...ts.infradead.org>, <dmaengine@...r.kernel.org>
Subject: Re: [PATCH v1] dmaengine: sf-pdma: pdma_desc memory leak fix

Hey Shravan,

On Fri, Jan 20, 2023 at 03:36:23PM +0530, shravan kumar wrote:
> From: Shravan Chippa <shravan.chippa@...rochip.com>
> 
> Commit b2cc5c465c2c ("dmaengine: sf-pdma: Add multithread support for a
> DMA channel") changed sf_pdma_prep_dma_memcpy() to unconditionally
> allocate a new sf_pdma_desc each time it is called.
> 
> The driver previously recycled descs, by checking the in_use flag, only
> allocating additional descs if the existing one was in use. This logic
> was removed in commit b2cc5c465c2c ("dmaengine: sf-pdma: Add multithread
> support for a DMA channel"), but sf_pdma_free_desc() was not changed to
> handle the new behaviour.
> 
> As a result, each time sf_pdma_prep_dma_memcpy() is called, the previous
> descriptor is leaked, over time leading to memory starvation:
> 
>   unreferenced object 0xffffffe008447300 (size 192):
>   comm "irq/39-mchp_dsc", pid 343, jiffies 4294906910 (age 981.200s)
>   hex dump (first 32 bytes):
>     00 00 00 ff 00 00 00 00 b8 c1 00 00 00 00 00 00  ................
>     00 00 70 08 10 00 00 00 00 00 00 c0 00 00 00 00  ..p.............
>   backtrace:
>     [<00000000064a04f4>] kmemleak_alloc+0x1e/0x28
>     [<00000000018927a7>] kmem_cache_alloc+0x11e/0x178
>     [<000000002aea8d16>] sf_pdma_prep_dma_memcpy+0x40/0x112
> 
> Add the missing kfree() to sf_pdma_free_desc(), and remove the redundant
> in_use flag.
> 
> Fixes: b2cc5c465c2c ("dmaengine: sf-pdma: Add multithread support for a DMA channel")
> Signed-off-by: Shravan Chippa <shravan.chippa@...rochip.com>

Reviewed-by: Conor Dooley <conor.dooley@...rochip.com>

Thanks,
Conor.


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